1. Field of the Invention
The invention relates generally to detecting radiation dose, and more specifically to a device for monitoring and evaluating radiological risks.
2. Description of the Prior Art
As a consequence of both the short-term health effects (radiation syndrome) and long-term health effects (a possibility of cancer later in life) of exposure to radiation, certain personnel who may be exposed to such radiation are required to wear radiation measurement devices 1) to measure accumulated dose and 2) to provide indication of accumulated dose while in radiation areas. The first device, a thermoluminescent dosimeter (TLD) is worn on the body, typically between the neck and waist to measure accumulated dose of beta and gamma radiation and must be processed by a dosimetry lab to determine a worker""s accumulated dose. A second device, a pocket dosimeter (pocket dosimeter) is typically worn next to the TLD for periodic visual indication of a worker""s accumulated gamma dose while in the radiation area. Pocket dosimeters typically measure 0 to 200 mrem, however, some high radiation pocket dosimeters are designed for measuring between 0 and 5 rem.
The pocket dosimeter of the prior art provides a viewing window with a scale (0 to 200 mrem typically) and a slim needle which moves upscale as gamma rays impact the charged sensor device inside. The dosimeter sensor device is fully charged initially to read 0 mrem. As gamma radiation impacts the dosimeter sensor element, the charge slowly dissipates, due to a capacitive discharge effect, and the needle moves to the right indicating a larger and larger accumulated dose.
Personnel may be assigned an xe2x80x9callotted dosexe2x80x9d (100 mrem, for example) before entering a radiation area along with a xe2x80x9cstay time.xe2x80x9d The allotted dose is determined by subtracting the worker""s accumulated dose to date for that calendar year from the yearly limit assigned to that worker at the beginning of the year and halving that to ensure the yearly limit is not exceeded. The stay time is determined by dividing a worker""s allotted dose by the expected exposure while in that area (typically based on the highest exposure rate in that work area). For example, if an individual has an allotted dose of 100 mrem and the work area to be entered has three sources of radiation (20 mrem/hour, 40 mrem/hour, and 100 mrem/hour) then the stay time will be equal to or less than 100 mrem/(100 mrem/hour)=1 hour. The denominator in this calculation is the highest value of the three radiation sources.
To be safe however, some facilities typically assign stay times of about xc2xd of what is permitted or 30 minutes in the foregoing example. Furthermore, to reduce the possibility of the pocket dosimeter going offscale and not having knowledge of a worker""s exposure until after their TLD is processed by the dosimetry lab, some protocols require that certain workers have their pocket dosimeters rezeroed before they exceed xc2xe scale or the 150 mrem point on a 0-200 mrem pocket dosimeter. In addition, some personnel are required to check their pocket dosimeter indicator every 10 to 20 minutes while in the radiological area. This requirement ensures that a worker is alerted of a high radiation situation before any radiological health risk is incurred. For example, if an area has a radiation source which emits 100 mrem per hour and the worker""s stay time/allotted dose are 1 hour/100 mrem, respectively, then it would be unexpected if after just 15 minutes the worker""s pocket dosimeter reads 90 mrem.
Pocket dosimeters of the prior art only provide an indication of accumulated dose and nothing else. Hence, personnel entering a radiation area must not only concentrate on and perform the task at hand, but they must continuously be mindful of the 10-minute interval check, conscious of their assigned stay time, watchful of their assigned allotted radiation dose, and watchful of the xc2xe scale point. From experience gained from the use of dosimeters of the prior art, it was considered that an improved radiological dosimeter could be developed to raise the level of safety by reducing the risk of overexposure while enabling improved concentration on work tasks for all radiation workers. Therefore, there is a need for smart dosimeters, which ate dosimeters incorporating dosage-triggered and time-triggered alarm features that allow the user to concentrate on the task at hand.
The radiation dose monitoring device, or smart radiological dosimeter of the present invention is designed to provide the same visual indication of accumulated gamma dose as pocket dosimeters in current use, with additional enhancements designed to give the radiological worker an extra level of assurance so that the worker can concentrate on the task at hand while the proposed invention takes on the burden of monitoring and evaluating the radiological risks encountered. The smart dosimeter provides and audible alarm indication to the user when their stay time (a predetermined time period) has elapsed, an audible reminder to check their dosimeter indication periodically for abnormal dose accumulation, an audible alarm indication indicating that their dosimeter has prematurely reached a predetermined accumulated dose (an xe2x80x9callotted dosexe2x80x9d limit that shouldn""t be reached based on their calculated stay time), and a means to ensure an audible alarm indication occurs prior to reaching the xc2xe scale point (a limit imposed to preclude the dosimeter from going off-scale).
This invention is an enhanced radiological accumulated dose measuring and monitoring system. It is a highly modified conventional pocket dosimeter instrument which incorporates a mobile miniature photoelectric optical sensor to detect the instant when the dosimeter needle arrives at a specific dose setpoint, a mechanical stop to limit the mobile sensor position to the xc2xe scale point, an amplifier and latch circuit to process the optical sensor output signal, a digital counter/timer circuit to indicate specific time setpoints, a small 4-digit LCD display with xe2x80x9cstay timexe2x80x9d programming pushbuttons, a watch-type battery, a miniature alarm (buzzer), and a reset switch.
In the present invention, these dosimeter features are consolidated into a compact package. The conventional dosimeter radiation sensing element internals are not affected. The optical sensors and miniature electronics of the dosimeter of the present invention are physically isolated from the sensing element components and are packaged in and around the view window end of the conventional dosimeter. In the present invention, these components are isolated from the sensing element because tapping off the charged sensing element signal can render the gamma measurement system inaccurate. Additionally, processing such low level charge signals into useable information requires additional complicated comparative and isolative electronics. The smart dosimeter system components are packaged into a wider flanged bottom in order to aid in anchoring the dosimeter in the worker""s pocket and to aid in preventing dosimeters from falling out of pockets.
With regard to package size, only the width of the dosimeter will increase. When workers are required to wear anti-contamination garments, this wider dosimeter can now be located in the flapped pocket adjacent to the conventional pocket dosimeter pocket which should represent no significant inconvenience to the worker. Finally, the proposed dosimeter can still be charged at the charging receptacle end of the dosimeter which is opposite the viewing window end and which is consistent with conventional dosimeter designs.